A known difficulty with the use of magnetic bearings is to supply power to the bearings during a system power failure, during which the power supply to the motor fails. While it is known to use auxiliary or back-up power supplies to the system, such as by way of batteries or the like, such auxiliary power supplies are relatively expensive and require additional switching controls to enable the auxiliary supply to take over when the main power supply fails. Further, the batteries have a limited life and generally must be replaced every two (2) years. This adds substantial further costs to the system.
It is therefore desirable to provide an improved power supply system for a high speed electric motor running in magnetic bearings which can maintain power to the bearings in the event of a main power supply failure.
It is also desirable to provide a power supply system for continuously supplying power to the magnetic bearings of a high speed electric motor following a failure of the main power supply until such time as the rotating parts are at rest.
It is also desirable to provide an improved controller for a high speed electric motor which enables a spinning rotor to spin down under controlled conditions.
It is also desirable to provide a power supply controller for a high speed electric motor with magnetic bearings which is relatively inexpensive, which is efficient in its operation and which provides a substantially fail-safe power supply for the magnetic bearings.